According to science, it is impossible to determine who the first person on earth was. This is because humans evolved from earlier primates over millions of years through a process of natural selection. However, scientists have identified several key moments in human evolution that led to the development of modern humans.

- Evolution of Homo sapiens
The evolution of Homo sapiens, or anatomically modern humans, began around 300,000 years ago in Africa. This species eventually spread throughout the world, replacing earlier human species such as Homo erectus and Neanderthals.

- Genetic Diversity
Genetic studies of modern humans have shown that humans today are descended from a small group of individuals who lived in Africa around 200,000 years ago. These individuals had a diverse range of genetic variations, which allowed them to adapt to different environments and survive.

- Fossil Records
Fossil records have also provided insights into the evolution of early humans. The oldest known human fossils, dated at around 2.8 million years old, were discovered in Ethiopia and belong to the species Australopithecus afarensis. This species is believed to be a direct ancestor of the Homo genus, which includes modern humans.

- Migration
As early humans evolved, they migrated out of Africa and spread throughout the world. This process of migration was driven by a variety of factors, including changes in climate and the availability of resources.

In conclusion, while it is impossible to determine who the first person on earth was, scientists have identified key moments in human evolution that led to the development of modern humans. These include the evolution of Homo sapiens, genetic diversity, fossil records, and migration.